Problem: $A=\left[\begin{array}{rr}8 & 6 & 3 & 9 & 5 \\2 & 1 & -14 & 12 & -4 \\6 &-18 &3 & -25 & -1 \\2 &4 &6 & -8 & 10\end{array}\right]$ $A_{4,5}=$
Explanation: Background An $m\times n$ matrix has $m$ rows and $n$ columns. $A=\left[\begin{array}{rr}A_{1,1} & \cdots & A_{1,n} \\\\\vdots \ & \ddots & \vdots \\\\A_{m,1} &\cdots &A_{m,n}\end{array}\right]$ Therefore, the entry $A_{{c},{d}}$ is located on row ${c}$ and column ${d}$. Finding $A_{4,5}$ $A_{{4},{5}}$ is located on row ${4}$ of $A$ : $\left[\begin{array}{rr}8 & 6 & 3 & 9 & 5 \\2 & 1 & -14 & 12 & -4 \\6 &-18 &3 & -25 & -1 \\ {2} & {4} & {6} & {-8} & {10}\end{array}\right]$ $A_{{4},{5}}$ is also located on column ${5}$ of $A$. $\left[\begin{array}{rr}8 & 6 & 3 & 9 & 5 \\2 & 1 & -14 & 12 & -4 \\6 &-18 &3 & -25 & -1 \\ {2} & {4} & {6} & {-8} & {\text{10}}\end{array}\right]$ Therefore, $A_{{4},{5}}={10}$. Summary $A_{4,5}=10$